This invention relates to an aqueous pressure-sensitive adhesive for use in adhesive tapes, labels, sheets, etc. (hereinafter these are collectively referred to as tapes).
In recent years, plastic products have become used widely and, for indicating their trademarks, prices, etc. thereon or for packaging or binding them, adhesive tapes using a pressure-sensitive adhesive are used. These tapes are usually removed when the plastic products are actually used. In the conventional pressure-sensitive adhesives, adhesion to adherend has been considered important, so that the adhesion to adherend has been so strong that when the tapes were removed from the adherend paper-breaking, adhesive-remaining on adherend, etc. tend to occur at the time of tape removal, resulting in staining of plastic product and significant deterioration of commercial value of plastic product. There are also pressure-sensitive adhesives which are generally called "peelable type" or "weak adhesion type" and which do not cause the paper-breaking or the adhesive-remaining on adherend; however, those of prior art remain as slight blur on adherend after the tapes using the adhesives have been removed. Pressure-sensitive adhesives remaining on adherend can be removed with a solvent or by mechanical rubbing when the adherend are metal or glass products; however, when the adherend is a plastic product, the surface of plastic product is sometimes attacked by the solvent or damaged by the mechanical rubbing, resulting in a significant deterioration of appearance or commercial value of plastic product at the time of its actual use.
The tapes are usually produced by coating a pressure-sensitive adhesive on a peeling paper, drying the adhesive-coated paper and transferring the adhesive onto a substrate such as paper, cloth, plastic film or the like. In the thus produced tapes, when the anchoring of the pressure-sensitive adhesive to the substrate (the paper) is poor, the pressure-sensitive adhesive is not peeled off from an adherend and only the substrate is peeled off when the tape is peeled off from the adherend, which eventually causes the adhesive-remaining on adherend. When the adhesion of the pressure-sensitive adhesive to the adherend is reduced in order to increase the peelability of the pressure-sensitive adhesive from the adherend, the anchoring of the pressure-sensitive adhesive to the substrate inevitably becomes poor and the same problem as mentioned above arises. Moreover, the peelability of a pressure-sensitive adhesive from an adherend decreases with time or with change in environmental conditions (e.g. heating) after the sticking of the tape on the adherend and also that the peelability depends on the type of the adherend. Thus, pressure-sensitive adhesives are required to be well balanced in adhesion to adherend, peelability from adherend and anchoring to substrate. Further, the peelability from adherend is required not to be influenced by the type of adherend and not to be reduced with time or with change in environmental conditions after sticking of tape on adherend. It is also required to be such that no blur on adherend is caused after the tape has been peeled off from the adherend. The conventional pressure-sensitive adhesives are far from satisfactory from these requirements.
In pressure-sensitive adhesives, the main component polymer is used generally in solution. For example, a polymer solution obtained by solution polymerization is used as such, or a polymer solution obtained by dissolving the formed polymer in a solvent is used. However, pressure-sensitive adhesives containing such a polymer solution have had problems such as toxicity, fire outbreak, environmental pollution and the like because the solvent contained in the polymer solution is removed by evaporation in the course of production of tapes from the adhesives.
Aqueous pressure-sensitive adhesives are known as an adhesive replacing the above solution type pressure-sensitive adhesives. As the aqueous pressure-sensitive adhesives, there are known, for example, an adhesive composition obtained by compounding a polyglycidylamine as a crosslinking agent with a carboxyl group-containing polymer (Japanese Patent Application Kokoku No. 57,509/82), an amino group-containing polymer obtained by using a specific functional monomer (Japanese Patent Application Kokai No. 93,460/74), an amino group-containing polymer obtained by using a tert-amino group-containing ethylenically unsaturated compound (Japanese Patent Application Kokai No. 134,032/75); an adhesive composition obtained by compounding an epoxy compound with a functional group-containing conjugated diene polymer (Japanese Patent Application Kokai No. 10,228/74); an adhesive composition obtained by compounding a water-soluble, high molecular weight substance and an epoxy compound with a carboxyl group-containing polymer (Japanese Patent Application Kokai No. 93,446/74); an adhesive composition obtained by compounding a phosphorous acid ester with an adhesive resin (Japanese Patent Application Kokai No. 243,669/87); and an adhesive composition obtained by compounding an amphoteric surfactant and a plasticizer with a copolymer emulsion (Japanese Patent Application Kokoku No. 47,463/87). These conventional pressure-sensitive adhesives of the solution type or the aqueous type do not satisfy the requirements that the pressure-sensitive adhesive is well balanced in the above-mentioned properties necessary for pressure-sensitive adhesive. Some of these conventional adhesives are fairly well balanced in said properties but they are such that blur remains on an adherend after the tapes having them are stuck on the adherend and then peeled off. Thus, a development of an improved aqueous pressure-sensitive adhesive has been desired.
Under such circumstances, the present inventors previously proposed, as an aqueous pressure-sensitive adhesive satisfying the requirements for pressure-sensitive adhesives, an adhesive composition obtained by compounding a polyglycidyl compound with a specific copolymer (Japanese Patent Application Kokai No. 86,777/88).